Dynamic light scattering (DLS)

Dynamic light scattering (DLS) is also known as photon correlation spectroscopy (PCS) or quasielastic light scattering (QELS). This method can determine the hydrodynamic radius of protein monomers, small aggregates in the nanometer range and partially also larger aggregates in the high nanometer/low micrometer range. Based on intensity fluctuations of laser light scattered by molecules/particles, moving in Brownian motion, the diffusion coefficient is determined and converted to particle size via the Stokes-Einstein equation.

As an advantage of DLS the protein monomer can be analyzed at the same time as larger aggregates. However, it needs to be considered that the intensity of the scattered light is proportional to the 6th power of the diameter. This makes DLS highly sensitive to detect minor amounts of aggregates. Therefore, intensity based size distributions often overestimate the presence of large aggregates and volume or number based distributions should additionally be considered.Analysis in a plate reader can save substantial amounts of time and material and the sample in the plate can even be re-used for example for fluorescence or UV spectroscopy. This is especially helpful for formulation screening. Analysis in a cuvette system provides even higher quality data connected with longer analysis time.

Independent of the used system, it needs to be noted that the viscosity of the sample influences the diffusion coefficient and thus the determined size. Therefore, knowledge of the viscosity is essential for DLS measurements. At Coriolis both cuvette (Malvern ZetaSizer Nano ZS) and plate reader (Wyatt DynaPro) systems are available.